A conventional open wrench is disclosed in U.S. Pat. No. 3,023,654 and Taiwan Patent Application No. 094220070, and generally includes an open wrench head having a recess and a hole is defined in the inside of the recess. The recess accommodates the bolt head which is rotated when the wrench is rotated. The hole is sealed by an end piece and a block and a spring are received in the hole. The two ends of the spring respectively bias the block and the end piece so as to provide a force to push the block toward the recess. A protrusion or a bent portion is defined in the recess and located close to the opening so as to prevent the block from dropping from the hole. The drawbacks are that the flange or bent portion has to be made and which has to be precisely located otherwise the movement of the block cannot be in contact with the head of the bolt, this could lead failure of the ratchet function of the wrench. The other drawback is that the flange decides the movement of the block and if the position of the flange is not correctly set, the driving head has to be cut to be thinner by precise cutting which generally is 0.5 mm cutting, and this may damage the driving head and increase the manufacturing cost.
The present invention intends to provide an open wrench which has simplified structure and reduces the manufacturing cost.